A new report has said State-funded broadcaster RTÉ is seriously deficient in Irish broadcasts.
An Coimisinéir Teanga has said the broadcaster is "seriously deficient, at odds with the will of the Oireachtas and in breach of the language provisions of the Broadcasting Act 2009".
An investigation by the commission found that less than 1% of programmes broadcast on RTÉ television are classified as Irish language programmes.
This is despite a statutory obligation to broadcast a comprehensive range of programmes in the language.
The investigation also found that some of the genres RTÉ is obliged to cover in Irish by the Broadcasting Act were either "not catered for at all" or only catered for in "a very limited fashion."
The report said that while RTÉ has a clear definition of what constitutes 'comprehensive coverage' in the English language, there appears to be a "drastically different understanding" of what this means in relation to its Irish language coverage.
An Coimisinéir Teanga Rónán Ó Domhnaill has recommended that RTÉ provides his office with an implementation plan, setting out the measures to be taken by the national broadcaster to ensure it meets its statutory language obligations.
Coimisinéir Ó Domhnaill said: "This is one of the most significant investigations conducted by my office since its foundation.
"This is the first time compliance with the Broadcasting Act, insofar as it relates to Irish language broadcasting, has been formally investigated.
"The results of the investigation reveal that only 0.7% of programmes broadcast on RTÉ television are classified as Irish language programmes.
"Or, in other words, approximately 99% of programmes are in English only."
Its annual report for 2018 also examined the inability of computer systems to use the síneadh fada - and a formal investigation, for the first time, into the use of Twitter for official purposes.
The investigations also looked Iarnród Éireann over its inability to use the síneadh fada on its on-board reservations system - as well as breaches of legislation in relation to signage.
It also examined Galway County Council regarding the issuing of tweets relating to the Gaeltacht, which were issued in English only.
It said: "This was in breach of its own statutory language scheme. It is also the first time a formal investigation by this office dealt with the use of Twitter."
The use of Google Translate on the Cork County Council website was also examined, which it found breached the statutory language obligation.
In total, the office received 634 complaints from members of the public last year - a slight decrease (0.63%) from 2017.
Most of the complaints related to the lack of Irish on websites, application forms, signage and stationery.